Stents are medical devices used for improving a stenosed or occluded lesion generated in a lumen in vivo, such as a blood vessel, bile duct, trachea, esophagus, urethra, etc. In general, a stent has a configuration in which a plurality of wavy annular bodies each formed in an annular shape from a wavy linear member are coaxially aligned and interconnected to obtain a network-like tubular body.
For instance, Japanese Patent Laid-open No. 2000-316983 describes a stent which has connection parts weaker than wavy annular bodies and which is formed in an overall tubular shape by interconnecting the adjacent wavy annular bodies by the connection parts. Even in the case where the stent is indwelled in a bifurcated blood vessel, after the stent is indwelled (i.e., placed in the blood vessel), a balloon catheter positioned inside the stent may pass through an opening in the network of the stent so that a portion of the balloon passes to the outside of the stent from the inside of the stent, and when the balloon is inflated, a connection part may rupture. This then requires an operation for putting a further stent indwelling in a branch blood vessel bifurcated from the bifurcated blood vessel.
Intensive and extensive investigations by the inventors here about the rupture of the connection part in the above-mentioned stent led to the discovery that only an extremely small part of the force exerted on the stent from the balloon acts on the connection part.
Specifically, in the process of rupturing the connection part, the balloon comes into contact with the wavy linear member while being inflated, and that part of the wavy linear member which extends slantly relative to the axial direction of the stent between a mountain crest portion and a valley bottom portion of the wavy linear member is pulled in a direction along the part. Therefore, the force exerted on the stent from the balloon acts on the connection part, mainly in a slanting manner relative to the axial direction of the stent (hereinafter, the direction that is slanted relative to the axial direction in which the force from the balloon acts mainly is referred to as the “main stress direction”). On the other hand, in the above-mentioned stent, the connection parts are formed parallel to the axial direction of the stent. Therefore, there is little possibility that the main stress direction and the direction of the connection part coincide with each other. This is why only an extremely small part of the force exerted on the stent from the balloon acts on the connection part in the known stent described above.
To permit easier rupture of the connection part, the connection parts may be formed to be weaker than necessary, which may lead to rupture of the connection parts at times other than at the time of balloon inflation. Or, in order to prevent the rupture of the connection parts from occurring at time other than the time of balloon inflation, the connection parts may be formed to have an enhanced rupture strength, which may make it difficult to rupture the connection part at the time of balloon inflation; in this case, there is a risk that an excessive expansive force may be exerted from the balloon.